ConnectionPool and AsyncConnectionPool remove the underlying __cause__ of the exception

[jhominal]

I have found that both synchronous and asynchronous connection pools will catch an error in handle_(async_)request and re-raise it while clearing out the __cause__ (with raise exc from None)

Why do we clear the __cause__ in this case? This is particularly bothersome for me because anyio does not usually set messages when raising BrokenResourceError (and other exceptions), and that results in me having only a httpcore.ReadError with an empty message, which is not very useful.

In other words: I would llike to modify that line in connection_pool so that __cause__ is not replaced with None, and so that the underlying error can appear when I collect tracebacks.